Fireproof building structure



Sept. 3, 1940.

J. H. YOUNG ET AL FIREPROOF BUILDING STRUCTURE E'i'led Oct. 14, 1958 INVENTORS 04.6 ATORHEY Qua,

Patented Sept. 3, 1940 UNITED STATES FIREPROOF BUILDING STRUCTURE.

\ James Howard Youngand Paul W. Jenkins, Pittsburgh, Pa., assignors to H. H. Robertson Company, Pittsburgh, Pa., a corporation of Pennsylvania Application October 14, 1938, Serial No. 235,020

2 Claims. (01. 712-70) This invention relates to a fireproof building structure.

The invention has for one object to produce a novel and fully fireproof building structure 5 embodying primary steel load supporting members, fireproofed by a relatively thin cementitious covering layer applied over metal lath secured to said load supporting member or members.

A further and more specific object of the invention is to provide a novel and highly efficient fireproof building structure embodying steel load supporting members fireproofed by a relatively thin layer of plaster applied over metal lath and in alayer thickness of the order of one inch from the face of the lath, which is further characterized by its lightness in Weight, not exceeding six pounds per square foot, and by an ability to remain in a substantially unaltered condition, and to maintain the temperature of the peratures required to cause failure of the members under full load when the fireproof building structure is subjected to a. standard fire test' conducted in accordance with the Standard Specifications for Fire Tests of Building Con struction and Materials (American Society for Testing Materials and the American Standards Association) With these objects in viewangl such others as may hereinafter appear, the 'itfi ention consists in the fireproof building structure and in the various combinations and arrangements of parts hereinafter described and particularly defined in the claims at the end of this specification.

In the drawing, Fig. his a cross-sectional end view of a portion pf afirlly fireproofed ceiling embodying the present invention; and Fig. 2 is a perspective view of a fully fireproofed structural column, shown in cross section and embodying and plaster applications has restricted the general use of such protection to so-called secondary fire-resistive structures. the problem of increasing the fire-resisting steel load supporing members below the tem-' members.

degree of fire resistance developed by single lath In attempting to solve characteristics of gypsum and other plaster, to

.the end that a single application of lath and plaster might be rendered capable of providing the desired fireproofing for satisfactory protection of primary steel load supporting members,

various forms of fillers including fibrous mate- 5 conditions, has been small in increasing the fireproofing efiiciency of lath and plaster systems and has not been suificient to gain acceptance for such as adequate fire protection for primary steel members in fully protected structures. The fire-resistive rating claimed is that measured in a standard fire test conducted in accordance with the Standard Specifications for Fire Tests of Building Construction and Materials (American Society for Testing Materials andthe American Standards Association)- We have found that exfoliated vermiculite when incorporated into the plaster, either gypsum, Portland cement or other equivalent plaster, in a substantial amount, produces a composition which, when applied in a single applica-' tion of lath and plaster to a steel structural member, produces a fireproofed structure which, when exposed to the tests and fire conditions requested by the building codes complies comstructures embodying primary load supporting Repeated tests have conclusively demonstrated that vermiculite plaster containing af substantial quantity of exfoliated vermiculite applied over metal lath in layers not exceedlng one inch in thickness from the lath and which may be successfully applied in accordance with standard plastering practice, cooper-' ates with aprimary load supporting member to form a-fully fireproofed structure capable of satisfactorily withstanding the exposure to the fire conditions required by the standard fire test above referred to. The particular reasons underlying these remarkable characteristics of vermiculite plaster are not entirely understood and the remarkable results were totally unexpected and unpredictable from any of the prior literature-involving the introduction of various fillers into gypsum and other plasters. It is recognized that others, prior to the present invention, have experimented with, and in pletely with the requirements for fully fireproof some instances used, vermiculite plaster compositions as, ordinary plaster over wood and equivalent structures but in no instance, however, as far as we can learn has this remarkable char--' acteristic of such vermiculite plaster composisubstantially unaltered condition when exposed.

. mated rating of two and one half hours .to steel tions been recognized and utilized in' producing available (at least from the standpoint of weight) a fully fireproofed structure embodying primary are indicative of the performance of materials steel load supporting members. The present inheretofore available. It is noted here that gypvention contemplates a fully fireproofed buildsum plaster as specified in the example of the'one ing structure embodying steel load supporting and one half hour rating. for fioors'refers to a members fireproofed by a relatively thin layer of stand'ard' mix of neat gypsum andsand developed vermiculite plaster applied over metal lath and for;the building industry and of prove'nability't'o in a layer of a thickness not exceeding an. inch withstand firegexposure in an efficient manner from the face of the lath and which cooperates within thelimitsof ratings established for it by with the steel load supporting members to fully fire test. It is also noted that the minimum fireproof the same and provide a structure in thickness of seven-eighths inch gypsum plaster which the thin layer of plaster, when subjected required under steel construction for a one and to fire conditions prescribed by the standard'fire one half hour rating represents about the practitests above referred to, operates to maintain the cal maximulm thickness of s'uch plaster as limited temperature of the steel load supporting memby cost off-application and the ability of the bers below those required to cause failureof the plaster to stay in place without an additional members under full load and to remain in a layer of metal lath asreinforcement.

to the fire conditions. field of use bf ordina gypsum plaster over metal The development of fireproof structures in this lath as fireproofing has been greatly st ed country ha mainly followed along. the line of because of the factthat the maximum thickness combining steel load-bearing members with heavy of plaster which could be app d u ssfu y and coverings and fillings of masonry, tile, concrete stay in place over metal lath was of the order of and-like combustible materials which have little one inch over the lath. Such a thickness of functional value other than in respect to fire- P aste did not afford thefireproofing q d by proofing. The enormous dead load factor introlaw for thefireproofing of primary load supportduced by these materials, and the absence of a suitable substitute for them, has been a major attempts have been made to improve charactering members and for a great/many years many deterrent to the development of eflicient and F st s of gypsum p s y difyin t e c meconomical steel frame buildings in the fireproof pos t thereof d y odu ti ther in f classification and has long been a problem in the ila us fi e None Of these, w v building industry. Metal-lath and plaster cover- S ved the p o The Procedure of pp y ing offers distinct advantages from the standdoub e lath and Plaster v ri g has been 8- point of weight added and of ease and cost of-- gested but the expense involved entirely preapplication in comparison with accepted fireeludes this procedure for general application and resistive coverings but the degree of fire-resistas a result the usual commonly accepted fully ance heretofore obtained with single lath and fireproof structure for primary load supporting plaster applications has limited their use for the members is typified by a two-inch thick reinprotection of steel members in buildings of secforced ypsu e Wit at east one lf inch of ondary fire-resistive types. gypsum plaster thereoifer. and such astructure is In illustration of present practice and as an given a four hour rating under the law. example of the protection heretofore obtained The present invention is based upon the unwith metal lath and plaster, model building codes usual perf rma e f titi us p a t mascribed a rating of one and one half hours to positions, preferably gypsum plaster composisteel joist floor construction consisting of a two o embodying Substantial a ou ts of o inch or more reinforced concrete or gypsum top plet'ely exfoliated vermiculite filler. Under test, slab and at least seven-eighths inch gypsum or a building structure having steel load supporting Portland cement plaster ceiling on expanded members fireproofed with metal lath and a one metal lath. The rating limits the use of this inch thick vermiculite plaster ceiling successfully relatively economical system of protection to withstood standard test fire conditions above rebuildings of secondary fire-resistive classification. e ed o pwards of five a d three-quarters The Building Code Committee of the United hou s, W e e Ordinary gyp um plaster under States Department of Commerce give an estisimilar conditions rates only one and one half hours. v

Referring now to the drawing, the invention has been illustrated as embodied in a fully fireing of at least one and one half inches or Portpro f d stru tur em dy p y steel load land cement mortar on metal lath furred-o'ut to supp rti g e e s Such as e flms furnish one inch air space between bottom flanges he I-beams II! have attached to the lower joist fioor construction when used with two inches or more top slab of cinder concrete and with ceilof joists and ceiling. A very few municipalities, flanges thereof metal lath I2 in any usual or prerequiring the minimum two and one half hour ferred manner anda-layer of vermiculite plaster resistive rating for floors also permit the use of is applied in accordance with ordinary plastering this thickness of gypsum plaster in similar conmethods over the metal lath to be secured therestruction but its absence from the Building Code to and form a prote underlying continuous Committee listing' indicates that there is no body of p a ter for t st u tu members ofllcial test data in support of the rating. Theupper surface of the I-beams may be pro- Steel joist construction similar to the above, tected by a similar layer of plaster or may be but with ceiling of two inch thick remforced gyp- L covered with the usual concrete'or other cementisum ceiling tile plus one half inch of gypsum tious layers as now commonly practiced. In plaster is commonly accepted as meeting the Fig. 2,.we have illustrated a column 20 havin requirements of fully protected construction; -A met'al lath covering the four sides thereof and four hour rating is generally extended similar attached thereto according to known methods. protection for structural beams, girders and Theinetal lath has applied to it vermiculite trusses. plaster of the order of thickness of one inch, the

The above examples, representing the most whole comprising a fully fireproofed structure. efiicient fire-resistive coveringsfor steel members It is preferred to utilize vermiculite plaster comprising a mixture of one part by weight of a standard vermiculite filler to three parts by weight of neat gypsum plaster. Such proportions represent a practical balance of such properties as plaster workability, density, hardness, drying time, thermal resistivity, resistance to shrinkage and disintegration in fire, and the like.

Mixes containing appreciably larger percentages proportions of filler and cementitious binder fromthe order of one to five parts by weight of neat gypsum plaster to one part by weight of expanded vermiculite.

The expanded vermiculite filler most successfully employed was Well graded from fine to coarse granules, not materially different in sizing from a representative grade of plastering sand. An approximate screen analysis showed 96% passing through a No. 14 screen, 56% through No. 28, 21% through No. and less than 5% through No. 100. Average loosevolume weight was 12 pounds per cubic foot. further characterized by the absence of unexpanded material capable of expansion a temperatures up to 1800" F. It is not intended that the invention be limited to this particular grade of expanded vermiculite as efiicient fireproofing qualities have been demonstrated with materials ,from other sources and of widely different particle size and range of particle size. The material employed does, however, represent the genral order of particle size which has been found to be most efiicient. from the standpoint of plastar workability and ease of application which are prime factors in determining the practicability of the plaster.

The weight of the preferred vermiculite plaster applied over metal lath to a thickness governed by one inch grounds and in accordance with standard plastering practice was found to be of the order of five and one-quarter pounds per square footof ceiling area. The same thickness of standard gypsum plaster rated at less It was than two and one half hours protection would weigh around 15. pounds. Gypsum tile protection required for fully protected construction of similar type would weigh around 15 pounds per square foot and from these comparative figures it will. be observed that the present fully fireproofed structure has the further desirable characteris tic of reducing to a minimum the dead load factor of the cementitious fireproofing.

While the preferred embodiment of the invention has been herein illustrated and described, it will be understood that the invention may be embodied in other forms within the scope of the following claims.

Having thus described the invention, what is claimed is:

1. In a building structure, in combination. a steel load bearing member, and a fireproof membrane mounted adjacent said member and between the same and a source of fire, said membrane comprising metal lath and a relatively thin cementitious layer containing exfoliated vermiculite and gypsum in proportion by weight of one part of vermiculite to from two to five parts of gypsum, said vermiculite having a particle size of ordinary plastering sand applied over the lath to a thickness not exceeding one inch, said membrane cooperating with the steel load supporting member to form a fully fireproof structure.

2. In a steel building structure embodying primary steel load supporting members, the combination with said primary steel load supporting members of a membrane carried by said-members and disposed to fireproof them against a source of fire and comprising metal. lath and gypsum vermiculite plaster embodying vermiculite having a particle size of ordinary plastering sand and in proportion by weight of one part of vermiculite to from two to five parts of gypsum, the thickness of said plaster not exceeding one inch and its Weight not exceeding six pounds .per square foot, said membrance being capable of fully fireproofing said primary load supporting members when the fireproof structure is tested under the conditions prescribed by the Standard Specifications for Fire Tests of Building Construction and Materials (American Society for Testing Materials and the American Standards Association).

JAMES HOWARD YOUNG.

PAUL W. JENKINS. 

